This invention relates generally to high voltage electrical transmission lines, and more particularly, to a compartmentalized gas insulated transmission line section.
Compressed gas insulated transmission lines are being used in an ever-increasing scale in recent years due to the desirability of increasing safety, their environmental acceptability, problems in acquiring right-of-way for overhead lines, higher power loads required by growing metropolitan areas and growing demands for electrical energy. Compressed gas insulated transmission lines typically comprise a hollow outer sheath, an inner conductor within the sheath, a plurality of insulating spacers which support the conductor, and a compressed gas such as sulfur hexafluoride or the like in the sheath to insulate the inner conductor from the outer sheath. The typical assembly has been fabricated from relatively short sections of hollow cylindrical ducts or tubes into which the conductor and insulators are inserted. This assembly is usually completed in the factory, and the sections are welded or otherwise secured together in the field to form transmission lines. It is also known to provide a particle trap in compressed gas insulated transmission lines as is disclosed in the patent to Trump, U.S. Pat. No. 3,515,939. The particle trap of Trump is utilized to allow conducting or semiconducting particles which could adversely affect the breakdown voltage of the dielectric gas to move from locations where such particles would cause breakdowns to locations where breakdown of the insulator gas is less likely to occur.
Problems have arisen, however, in the use of such compressed gas insulated lines. Occasionally, not all of the particles are captured in the particle traps, but contamination particles may sometimes collect on the insulating spacer surfaces and initiate high voltage flashover. To decrease the probability of this happening, it is desirable that the spacer surface area upon which the particles could collect be made as small as possible. This desire to minimize the surface area of the spacer has resulted in the use of post-type insulating spacers to support the inner conductor.
However, the use of such post-type spacers presents an additional problem; if, in the unlikely event of a failure in the line with resulting breakdown and arcing, arc products or contamination may occur, and this contamination and arc product can migrate from the section of the transmission line where they occurred to adjacent sections. This movement of arc products and contamination throughout the transmission line may then cause subsequent substantial damage. One manner of avoiding this problem is, instead of utilizing post-type insulating spacers, to use conical or disc spacers. These conical or disc spacers block the progress of arc products or contamination along the line. But the use of such conical or disc spacers present again the problem of having a large surface area upon which particles may collect and initiate flashover. Also, such spacers may restrict gas flow and evacuation, and are more expensive than the post-type insulating spacers.